June 1, 2015: Equine Encephalitides

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June 1, 2015

Equine Encephalitides

The summer and fall seasons in North America herald outbreaks of viral zoonotic encephalitis. An important subset of infectious agents includes the equine encephalitides: Eastern, Western, and Venezuelan equine encephalitis. There geographic distribution is broad, with human cases of Eastern equine encephalitis reported in the East Coast, Gulf Coast, Midwest, and Texas; cases of Western equine encephalitis reported in Florida and most states west of the Mississippi; and, cases of Venezuelan equine encephalitis reported primarily in Central and South America(1). The equine encephalitides are a rare cause of disease in humans, with Eastern equine encephalitis being the most common and most virulent in the United States, with the mortality rate approaching 35%(1). Symptoms are nonspecific and include fever, malaise and myalgia beginning three to 10 days after a mosquito exposure, and progressing to headache, confusion, and seizures. Treatment is primarily supportive, with consideration of corticosteroids and anticonvulsants when indicated(2). Cases are confirmed with serum and CSF serologies(2).


  1. Go YY, Balasuriya UB, Lee CK. Zoonotic encephalitides caused by arboviruses: transmission and epidemiology of alphaviruses and flaviviruses. Clinical and Experimental Vaccine Research 2014; 3: 58-77.
  2. Davis LE, Beckham JD, Tyler KL. North America encephalitic arboviruses. Neurologic Clinics 2008; 26: 727-757.

Submitted by Adam Numis, MD, Department of Neurology, University of California, Los Angeles.

Disclosures: Dr. Numis is a member of the Residents & Fellows Section of Neurology.

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